Optical fibre microlens and optical radiation source employing the same
Embodiments of the present invention provide optical fibre microlenses having anamorphic focusing means which have a major axis which is not perpendicular to the longitudinal axis of the optical fibre. In particular, a wedge-shaped optical fibre microlens whose tip is skewed with respect to the longitudinal axis of the optical fibre, is described. Such optical fibre microlenses find particular application in coupling light from semiconductor lasers having asymmetrical output radiation patterns, since they increase the coupling efficiency and reduce the level of back reflection from the microlens to the laser. This is of particular importance for semiconductor lasers used to pump optical fibre amplifiers.
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Claims
1. An optical fibre microlens comprising anamorphic focusing means integrally formed on an end of said optical fibre, said anamorphic focussing means having a major axis that is non-perpendicular to a longitudinal axis of the optical fibre.
2. An optical fibre microlens as claimed in claim 1, wherein the anamorphic focusing means is substantially circularly cylindrical and the major axis of the focusing means comprises the axis of the cylinder.
3. An optical fibre microlens as claimed in claim 1, wherein the anamorphic focusing means comprises at least two substantially planar surfaces inclined with respect to each other to form a wedge, and the line of intersection of the two planar surfaces at the tip of the wedge comprises the major axis of the focusing means.
4. An optical fibre microlens as claimed in claim 3, wherein the profile of the tip of the wedge, in a plane perpendicular to the line of intersection of the two planar surfaces, is curved.
5. An optical fibre microlens as claimed in claim 4, wherein the asymptotes of the profile of the tip of the wedge lie within the two planar surfaces.
6. An optical fibre microlens as claimed in claim 4, wherein the profile is substantially hyperbolic.
7. An optical fibre microlens as claimed in claim 4, wherein the profile is substantially circular.
8. An optical fibre microlens as claimed in claim 3, wherein the angle (.phi.) between the two planar surfaces is between 95.degree. C. and 125.degree. C.
9. An optical fibre microlens as claimed in claim 3, wherein the tip of the wedge is truncated in the vicinity of the longitudinal axis of the optical fibre.
10. An optical fibre microlens as claimed in claim 9, wherein the tip of the wedge is truncated by a third substantially planar surface inclined at a substantially equal angle to each of the at least two substantially planar surfaces.
11. An optical fibre microlens as claimed in claim 1, wherein the angle (.theta.) between the major axis of the focusing means and the axis of the optical fibre is less than 89.degree. C. and greater than 75.degree. C.
12. An optical fibre microlens as claimed in claim 11, wherein the angle (.theta.) between the major axis of the focusing means and the axis of the optical fibre is substantially 83.degree. C.
13. A source of optical radiation comprising a semiconductor laser diode, having an output facet, and an optical fibre microlens as claimed in claim 1, aligned to receive optical radiation output from an active area of the laser diode through the output facet, wherein the level of optical radiation, output from the laser diode, which is reflected back from the microlens to the active area of the laser diode is substantially reduced.
14. A source of optical radiation as claimed in claim 13, wherein the longitudinal axis of the optical fibre is not perpendicular to the output facet of the semiconductor laser diode.
15. A source of optical radiation as claimed in claim 14, wherein the longitudinal axis of the optical fibre makes an angle (90-.psi.) of between 89.degree. C. and 83.degree. C. with the output facet of the semiconductor laser diode.
16. A source of optical radiation as claimed in claim 14, wherein the longitudinal axis of the optical fibre makes an angle (90-.psi.) of substantially 87.degree. C. with the output facet of the semiconductor laser diode.
17. A source of optical radiation as claimed in claim 13, wherein the angle (.omega.) between the line of intersection of the two planar surfaces of the microlens and the output facet of the laser diode is between 5.degree. C. and 15.degree. C.
18. A source of optical radiation as claimed in claim 17, wherein the angle (.omega.) between the line of intersection of the two planar surfaces of the microlens and the output facet of the laser diode is approximately 10.degree. C.
19. A source of optical radiation as claimed in claim 13, wherein the wavelength of the optical radiation output from the laser diode is suitable for pumping a rare earth doped optical fibre amplifier, or laser.
20. A source of optical radiation as claimed in claim 13, wherein the wavelength of the optical radiation output from the laser diode is suitable for pumping an erbium doped optical fibre amplifier, or laser.
21. A source of optical radiation as claimed in claim 13, wherein the wavelength of the optical radiation output from the laser diode is substantially 980 nm.
22. A method of forming an optical fibre microlens on an end of an optical fibre, the method comprising the steps of:
- i) mounting an optical fibre into a holder at an angle (90-.theta.) to a rotational axis of the holder,
- ii) grinding a first surface on the end of the optical fibre,
- iii) rotating the holder through substantially 180.degree. C. about its rotational axis, and
- iv) grinding a second surface on the end of the optical fibre.
23. A method as claimed in claim 22, comprising the further steps of:
- v) checking the quality of the optical fibre microlens by passing optical radiation through it, and
- vi) repeating steps ii) to v) until the desired quality is achieved.
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Type: Grant
Filed: Jul 16, 1997
Date of Patent: Aug 17, 1999
Assignee: Hewlett-Packard Company (Palo Alto, CA)
Inventor: Andrew Thomas Harker (Suffolk)
Primary Examiner: John D. Lee
Assistant Examiner: Juliana K. Kang
Application Number: 8/892,961
International Classification: G02B 625; G02B 632;